The present invention relates to a device for automatically operating a vehicle, or for providing a vehicle driver with road information in support of the driving activity, and a system for controlling a moving vehicle employing such device. More specifically, the present invention relates to an electric resonance element buried in a road, a detection apparatus for detecting the electric resonance element, and a system which includes the above items for controlling a moving vehicle.
Information about roads and information needed for driving a vehicle has been exhibited to a driver by means of a lane mark, a road sign and the like. These are recognized by the vehicle driver by using his eyes. However, it may be not easy to recognize and understand the information through the human eyes especially during rough weather or at night. The safety of vehicle drivers under such circumstances has not been assured.
Experiments are under way for an automatic vehicle driving system. In such a system, a sensor installed in a vehicle detects magnetic markers provided on a road and an automatic driving equipment controls the vehicle based on information delivered from the sensor. The sensor uses magnetics. Such a sensor, however, has a relatively great possibility of errors due to magnetic turbulence. Therefore, a system that assists in the driving of a vehicle by exchange of information by means of electromagnetic waves would be desirable.
Among the information exchange means using electromagnetic waves is a method that uses the phenomenon of electric resonance. The method has been in use as an anti-theft system used in retail shops for preventing the stealing of a merchandise. The system comprises an electric resonator shaped in the form of a film, which is attached to merchandise, and a detection apparatus disposed at the exit of shop. The film-shaped electric resonator comprises a coil made from metal foil and a chip capacitor.
Under the above described system, however, only an electric resonance of high frequency can be used, because the inductance of the coil made from metal foil is small and the capacitance of the chip capacitor is small. For the above reasons, a detection method based on the electric resonance phenomenon normally uses an electromagnetic wave of several megahertz, and the detection is conducted through a phase detection method.
In the above described conventional detection apparatus using the electric resonance phenomenon, however, the level of an input signal of an electromagnetic wave transmitted from an electric resonance element detected at the detector is extremely small as compared with the output level of a call-on electromagnetic wave transmitted (hereinafter called as transmitting wave). As a result, it is difficult to detect the phase of an input signal based on the phase of the transmission wave.
Described practically, the signal level of an input signal at the above described detection apparatus is normally about several millionths of that of the transmitting wave. This means that if a detection apparatus is located away from an electric resonance element, it can not detect the signal, and the directivity of the signal is not sufficient either. Especially, in a case where a transmitting antenna and a receiving antenna are independently provided, a substantial interference is caused by the transmitting wave on the receiving.
An electric resonance element in accordance with an exemplary embodiment of the present invention (hereinafter referred to as resonance device) comprises a coil and a capacitor which determine a frequency of a specific electric resonance (resonance frequency), and a magnetic core having an approximately plate or rod shape which concentrates and selectively amplifies the high frequency magnetic flux of a transmitting wave. The invented resonance device is housed in a sealed vessel provided for protecting the capacitor, core, etc. from deterioration.
A detection apparatus for detecting the electric resonance element in accordance with an exemplary embodiment of the present invention (hereinafter referred to as detection apparatus) comprises a transmitting section for transmitting an electromagnetic wave of the resonance frequency of said resonance device, a receiving section for detecting an electromagnetic wave transmitted from the resonance device, and means for keeping the receiving section inert while the transmitting section is transmitting the electromagnetic wave of the resonance frequency.
An exemplary transmitting section comprises:
a) a discharge resistor for instantaneously suspending transmission of a signal when the detection apparatus is alternated to a receiving made from a transmitting mode,
b) a function of transmitting electromagnetic waves in a plurality of frequencies,
c) tuning capacitors corresponding to a plurality of resonance frequencies, and
d) means to select a tuning capacitor among the tuning capacitors in accordance with the resonance frequency to be oscillated.
An exemplary receiving section comprises:
a) a loop antenna shaped in the form of a figure eight, for efficiently receiving an electromagnetic wave oscillated from a resonance device,
b) a local oscillator,
c) a frequency converter for converting an electromagnetic wave received at the receiving section oscillated from an resonance device and a frequency oscillated from the local oscillator into a certain specific frequency (intermediate frequency), and
d) a detecting section for detecting the level of electromagnetic wave of the intermediate frequency.
Other exemplary detection apparatus of the present invention may be formed by using a direct digital synthesizer for the local oscillator, which oscillates a frequency of the transmitting wave, as well as a frequency identical to the difference between the intermediate frequency and the transmitting frequency during receiving.
After exchanging a signal using an electromagnetic wave of a certain resonance frequency among the plurality of resonance frequencies, an invented detection apparatus can exchange signals by using other electromagnetic waves of different frequencies other than the one resonance frequency. Thus those signals oscillated from a plurality of resonance devices are detected with high reliability.
An system for controlling a moving vehicle comprises the above described resonance device buried in a road; with which system, a vehicle equipped with the above described detection apparatus automatically detects the resonance device, or the system provides a vehicle driver with driving support.